FIG. 7 shows a circuit configuration of a conventional lighting device. As shown in FIG. 7, in this conventional lighting device, an AC power of a commercial power source 101 is rectified to a DC power by a rectifier 102. After this DC power is smoothed by a smoothing capacitor 103 and then converted to an AC power by an inverter main circuit 104, the AC power is supplied to a discharge lamp 106. A main control circuit 105 is operable to control an operation of the inverter main circuit 104 so that the AC power to be supplied to the discharge lamp 106 is controlled in a desired manner.
The smoothing capacitor 103 requires having a large capacitance. Thus, an aluminum foil electrolytic capacitor is typically used as the smoothing capacitor 103. In the aluminum foil electrolytic capacitor, an electrochemical reaction is produced thereinside, and thereby the capacitance will be reduced along with an increase in operating time. This causes a problem about deterioration in the original smoothing function and increase in loss, and its lifetime is limited to a certain period (e.g., guaranteed life: 12000 hours at 105° C.). As above, the lifetime of the aluminum foil electrolytic capacitor is shorter than other electronic components, and thereby a lifetime of the lighting device is determined by the aluminum foil electrolytic capacitor.
Therefore, for example, in an inverter device for a motor as a load, there has been known one type designed such that a voltage across both ends (i.e., both-end voltage) of an aluminum foil electrolytic capacitor (smoothing capacitor) is measured after an elapse of a given time from a time when the both-end voltage is lowered to a given value during shutoff of power input to an inverter main circuit or occurrence of a power interruption, and a life end of the smoothing capacitor is determined depending on whether the measured both-end voltage is equal to or less than a threshold value. Further, this inverter device is operable, when the measured both-end voltage is equal to or less than the threshold value, to annunciate the life end of the smoothing capacitor (see, for example, the following Patent Publication 1).
There has been proposed another inverter device designed to measure a discharge time of a smoothing capacitor during shutoff of power input to an inverter main circuit, and annunciate a life end of the smoothing capacitor when the discharge time becomes equal to or less than a predetermined threshold value (see, for example, the following Patent Publication 2).
There has been proposed yet another inverter device designed to detect a ripple voltage or ripple current of a smoothing capacitor, and perform a determination on a life end of the smoothing capacitor based on a result of a comparison between the detected ripple voltage or current and a predetermined value (see, for example, the following Patent Publication 3).
Patent Publication 1: JP 8-80055 A
Patent Publication 2: Japanese Patent No. 3324239
Patent Publication 3: JP 7-222436 A